Time-resolved Absorption Spectroscopy Diagnosis Of Ar Metastable

Time-resolved tunable diode laser absorption spectroscopy of Ar(1s5,1s3)metastable number density and gas temperature was studied.In dielectric barrier discharge of plasma,the central frequency of the AC power supply was 2 kHz,which the tunable range was about20%-30% up and down.In order to ensure that the laser scanning and discharge were synchronous such a setup was made: a voltage signal of oscilloscope obtained by a high voltage probe was used as an output trigger signal,and the signal generator received this signal to trigger the laser,then the laser started to scan.Finally,the average of 20 experimental results was completed,the experimental error was reduced.The number density of metastable Ar was obtained based on the absorption law of Lambert-Beer and the absorption peak area obtained by Voigt fitting,the temperature was got by Doppler broadening.The results show that:(1)There are two absorption peaks in one discharge cycle and because only one electrode was covered with a dielectric plate(quartz glass),the peaks of the two positions were asymmetric.In addition,the temperature and density of metastable Ar declined in different times,which was due to the discharge being not completely extinguished.(2)As the pressure increasing,the number density increased gradually because of the collision between particles,similar to the change in pressure,the number density increased with the increasing of gas flow.In addition,the number density increased with the increasing of discharge voltage.Finally,the increase of the electrode spacing and the different laser beam position had great influences on the number density.Number density decreased with distance increasing in negative half discharge cycle,while it was the opposite phenomenon in positive half cycle.(3)It is found that gas temperature decreased with gas pressure increasing,while the change is not obvious with flow and discharge voltage increasing,because the range of conditions were small.